Why does my electric bill change from month to month?
Your electric bill is based on your electricity usage, which is measured in kilowatt hours (kWh). Your usage fluctuates from month to month depending on the number of items in your home that use electricity, the efficiency of these items, and how much they are used.
The amount of electricity an appliance uses varies depending on its age and features. For example, an air conditioner that is 10 years old uses more electricity to run than it’s new, energy efficient counterpart.
Overall electricity usage also tends to vary seasonally with the highest usage occurring in the summer and the winter.
Here are just some of the items that impact electricity usage more than expected. The level of impact varies significantly depending on the item:
- Home heating system – even a forced hot air system that runs on gas uses electric motors to circulate the hot air
- Space heaters & electric fire places
- Roof coils for melting snow/ice during the winter
- Heated bathroom floors
- Heated driveways
- Holiday Lights
- Central air system/air conditioners
- Sump pumps
- Humidifiers and Dehumidifiers
- Pool pumps
- Outdoor fish ponds/water fountains with electric pumps
- Ceiling fans
- Electric hot water heaters
- Dishwashers, particularly when using the heat dry feature
- A second refrigerator or freezer in the home
- Hot tubs
- Air purifiers
- Fish tanks/reptile terrariums
- Video game consoles
- House guests
For tips on reducing your home’s energy use, click here.
How much electricity do my appliances use?
Nowadays, it’s difficult to provide a general estimate of how much it costs to run an appliance (a refrigerator, for example) because there are so many variables such as age, features, energy efficiency, size, etc. However, if you’re interested in knowing about how much it costs to run the appliances in your home, there are ways to estimate how much electricity they use as well as the monthly cost.
Energy Guide Label
The easiest way to determine this is to check the Energy Guide label that may have come with the appliance. The label provides an estimate of the cost based on average usage. However, this cost will vary based on actual usage and utility rates, and not all appliances come with the label.
Electricity Usage Monitor
Another option is to use an electricity usage monitor. Simply plug the monitor into an electrical outlet and then plug the appliance into the monitor. The display on the monitor will provide information about the appliance including how many watts it’s using. The monitor can also tell you how many kilowatt hours (kWh) the appliance uses over a period of time. It’s important to note that these monitors only work with appliances that are the standard 120-volt, so you would not be able to use it to measure the energy usage of larger appliances such as a clothes dryer or water heater.
RMLD has provided two Home Energy Evaluation Kits to each library in our service area – each kit contains an energy usage monitor and helpful reference materials. These kits are available for checkout with a local library card. Energy usage monitors are also available for purchase at a relatively low cost online or at any local home improvement/hardware store.
Calculating the Cost
One alternative is to do the math yourself using a few simple formulas. First, you’ll need to find the appliance’s wattage. The wattage value can often be found written somewhere on the appliance. If amperage is listed on the appliance rather than wattage, wattage can be calculated by multiplying amperage by the appliance voltage. Most appliances in the U.S. use 120 volts, with the exception of some larger appliances such as clothes dryers. The formula looks like this:
Wattage = Amperage × Voltage (usually 120)
Once you have the wattage, use these formulas to determine usage and cost:
Example using Pool Pump
(1.5 Horsepower/2,250 Watt)
Daily kWh Consumption = (Wattage × Number of hours per day the appliance runs) ÷ 1,000
Daily kWh Consumption = (2,250 Watts × 8 hours per day) ÷ 1,000 = 18 kWh
Monthly kWh Consumption = Daily kWh Consumption × Number of Days Used per Month
Monthly kWh Consumption = 18 Daily kWh × 30 Days Used per Month = 540 kWh
Monthly Cost = Monthly kWh Consumption × Cost per kWh (This fluctuates based on RMLD’s actual purchased power costs - Click here to see instructions on calculating cost per kWh).
Monthly Cost = 540 Monthly kWh × RMLD Residential Rate of $0.163 kWh = $88.02
Please note, it’s important to use the wattage listed on your appliance to get the most accurate results. It’s also important to note that the results of this calculation are unlikely to be 100% accurate because your usage may vary slightly from day-to-day. For example, you may estimate that you watch TV for 1.5 hours per day, but it’s likely that there are days when you watch a bit more and days when you don’t watch TV at all. For the most accurate results, keep a log of your usage.
What can I do to understand my overall usage?
Request a No-Cost Home Energy Assessment
RMLD offers no-cost home energy assessments to residential customers who are interested in implementing energy efficiency and conservation measures. The assessment consists of an evaluation of the home to identify efficiency measures that will help to conserve energy and lower your electric bill. Information about the various residential rebate programs is also provided.
To request a Home Energy Assessment, please contact RMLD's provider, Energy New England, at 888-772-4242.
PLEASE NOTE: If you are a served by a gas utility that is a Mass Save member (such as National Grid), we recommend that you obtain a home energy assessment through Mass Save because it will evaluate items in your home that are specific to your heating type. Visit Mass Save's website to schedule.
Install a Whole-House Energy Monitoring System
You also have the option of installing a whole-house energy monitoring system. These systems measure energy use by circuit and also have the ability to measure larger appliances that use 240-volts. These systems are typically installed in the main breaker panel of the home, usually by an electrician. Costs vary by system and features but will be significantly more than an electricity use monitor that plugs into an outlet.